Method and apparatus for supporting data synchronization for 4g/5g dual-registered mobile communication terminal

ABSTRACT

The present disclosure relates to a pre-5th-Generation (5G) or 5G communication system to be provided for supporting higher data rates Beyond 4th-Generation (4G) communication system such as Long Term Evolution (LTE). The embodiments in the present disclosure allow to transfer remaining data between different base stations in a dual-registration interworking process, which provides terminal mobility between 4G and 5G networks without a data loss. Further, it provides the terminal mobility with no data loss without changing 5G and 4G base station implementation through addition of a simple function of new equipment, such as SMF and UPF. Further, it supports different QoS and forwarding path units in the 5G/4G networks without changing 5G and 4G base station functions. Further, it exempts additional function implementation costs for re-ordering in a terminal and a network through in-order delivery of packets to the terminal without changing the packet order during 4G-5G network movement.

CROSS-REFERENCE TO RELATED APPLICATION AND CLAIM OF PRIORITY

This application is based on and claims priority under 35 U.S.C. § 119to Korea Patent Application No. 10-2017-0102950 filed on Aug. 14, 2017,in the Korea Intellectual Property Office, the disclosure of which isincorporated by reference herein in its entirety.

BACKGROUND 1. Field

The present disclosure relates to an apparatus for providing a servicewithout a data loss in a process where a terminal moves between 5G and4G mobile communication systems and an operation method thereof.

2. Description of Related Art

To meet the demand for wireless data traffic having increased sincedeployment of 4G communication systems, efforts have been made todevelop an improved 5G or pre-5G communication system. Therefore, the 5Gor pre-5G communication system is also called a ‘Beyond 4G Network’ or a‘Post LTE System’.

The 5G communication system is considered to be implemented in higherfrequency (mmWave) bands, e.g., 60 GHz bands, so as to accomplish higherdata rates. To decrease propagation loss of the radio waves and increasethe transmission distance, the beamforming, massive multiple-inputmultiple-output (MIMO), Full Dimensional MIMO (FD-MIMO), array antenna,an analog beam forming, large scale antenna techniques are discussed in5G communication systems.

In addition, in 5G communication systems, development for system networkimprovement is under way based on advanced small cells, cloud RadioAccess Networks (RANs), ultra-dense networks, device-to-device (D2D)communication, wireless backhaul, moving network, cooperativecommunication, Coordinated Multi-Points (CoMP), reception-endinterference cancellation and the like.

In the 5G system, Hybrid FSK and QAM Modulation (FQAM) and slidingwindow superposition coding (SWSC) as an advanced coding modulation(ACM), and filter bank multi carrier (FBMC), non-orthogonal multipleaccess (NOMA), and sparse code multiple access (SCMA) as an advancedaccess technology have been developed.

On the other hand, in a general communication system, information forconfiguring a data forwarding path for data synchronization istransferred in an inter-eNB handover procedure. However, in case ofdual-registration interworking, since terminal mobility is supported bya connection procedure between a terminal and a network withouttransferring an inter-eNB handover signal, it is difficult to apply ageneral communication technology thereto. Accordingly, there has been aneed for schemes for solving this.

SUMMARY

Aspects of the present disclosure propose a data synchronization schemefor supporting terminal mobility between 4G and 5G networks without apacket loss through non-use of a handover signal procedure duringapplication of dual-registration interworking. If a terminal movesbetween the 4G and 5G networks through application of the proposedscheme, it becomes possible to provide seamless services without a dataloss.

In accordance with an aspect of the present disclosure, a method forcontrolling a first entity in a wireless communication system includesreceiving a data forwarding request from a second entity through amovement of a terminal from a first network to a second network;configuring a data forwarding path between the first entity and a firstnetwork base station based on the received data forwarding request, andtransmitting information on the configured data forwarding path to thefirst network base station; receiving data packets from the firstnetwork base station based on the configured data forwarding path; andforwarding the received data packets through a path established withrespect to a second network base station.

In accordance with another aspect of the present disclosure, a methodfor controlling a first network base station in a wireless communicationsystem includes receiving, if a first entity receives a data forwardingrequest from a second entity through a movement of a terminal from afirst network to a second network, configuration information on a dataforwarding path between the first entity and the first network basestation from the first entity based on the received data forwardingrequest; establishing the data forwarding path based on theconfiguration information; and transmitting data packets that have notbeen transmitted to the terminal to the first entity through theestablished data forwarding path, wherein the data packets are forwardedby the first entity through a path established with respect to a secondnetwork base station.

In accordance with still another aspect of the present disclosure, afirst entity in a wireless communication system is provided. The firstentity is configured to receive a data forwarding request from a secondentity through a movement of a terminal from a first network to a secondnetwork, configure a data forwarding path between the first entity and afirst network base station based on the received data forwarding requestand transmit information on the configured data forwarding path to thefirst network base station, receive data packets from the first networkbase station based on the configured data forwarding path, and forwardthe received data packets through a path established with respect to asecond network base station.

In accordance with yet still another aspect of the present disclosure, afirst network base station in a wireless communication system isprovided. The first network base station is configured to receive, if afirst entity receives a data forwarding request from a second entitythrough a movement of a terminal from a first network to a secondnetwork, configuration information on a data forwarding path between thefirst entity and the first network base station from the first entitybased on the received data forwarding request, establish the dataforwarding path based on the configuration information, and transmitdata packets that have not been transmitted to the terminal to the firstentity through the established data forwarding path, wherein the datapackets are forwarded by the first entity through a path establishedwith respect to a second network base station.

According to the aspects of the present disclosure, it is possible totransfer the remaining data between different base stations in thedual-registration interworking process, and thus it becomes possible toprovide the terminal mobility between the 4G and 5G networks without thedata loss.

Further, it becomes possible to provide the terminal mobility with nodata loss without changing the 5G and 4G base station implementationthrough addition of a simple function of new equipment, such as asession management function (SMF) device and a user plane function (UPF)device.

Further, it becomes possible to support different QoS and forwardingpath units in 5G and 4G networks without changing 5G and 4G base stationfunctions.

Further, it becomes possible to exempt additional functionimplementation costs for re-ordering in the terminal and the networkthrough in-order delivery of packets to the terminal without changingthe packet order during 4G-5G network movement.

Before undertaking the DETAILED DESCRIPTION below, it may beadvantageous to set forth definitions of certain words and phrases usedthroughout this patent document: the terms “include” and “comprise,” aswell as derivatives thereof, mean inclusion without limitation; the term“or,” is inclusive, meaning and/or; the phrases “associated with” and“associated therewith,” as well as derivatives thereof, may mean toinclude, be included within, interconnect with, contain, be containedwithin, connect to or with, couple to or with, be communicable with,cooperate with, interleave, juxtapose, be proximate to, be bound to orwith, have, have a property of, or the like; and the term “controller”means any device, system or part thereof that controls at least oneoperation, such a device may be implemented in hardware, firmware orsoftware, or some combination of at least two of the same. It should benoted that the functionality associated with any particular controllermay be centralized or distributed, whether locally or remotely.

Moreover, various functions described below can be implemented orsupported by one or more computer programs, each of which is formed fromcomputer readable program code and embodied in a computer readablemedium. The terms “application” and “program” refer to one or morecomputer programs, software components, sets of instructions,procedures, functions, objects, classes, instances, related data, or aportion thereof adapted for implementation in a suitable computerreadable program code. The phrase “computer readable program code”includes any type of computer code, including source code, object code,and executable code. The phrase “computer readable medium” includes anytype of medium capable of being accessed by a computer, such as readonly memory (ROM), random access memory (RAM), a hard disk drive, acompact disc (CD), a digital video disc (DVD), or any other type ofmemory. A “non-transitory” computer readable medium excludes wired,wireless, optical, or other communication links that transporttransitory electrical or other signals. A non-transitory computerreadable medium includes media where data can be permanently stored andmedia where data can be stored and later overwritten, such as arewritable optical disc or an erasable memory device.

Definitions for certain words and phrases are provided throughout thispatent document, those of ordinary skill in the art should understandthat in many, if not most instances, such definitions apply to prior, aswell as future uses of such defined words and phrases.

BRIEF DESCRIPTION OF THE DRAWINGS

For a more complete understanding of the present disclosure and itsadvantages, reference is now made to the following description taken inconjunction with the accompanying drawings, in which like referencenumerals represent like parts:

FIG. 1A is an exemplary diagram illustrating the 4G-5G interworkingnetwork structure based on single registration;

FIG. 1B is an exemplary diagram illustrating the 4G-5G interworkingnetwork structure based on dual registration;

FIG. 2 is an exemplary diagram explaining the operational conceptaccording to an embodiment of the present disclosure;

FIG. 3 is an exemplary sequence diagram illustrating an operation schemeof the present disclosure when a terminal moves from a 5G network to a4G network according to an embodiment of the present disclosure;

FIG. 4 is an exemplary sequence diagram illustrating an operation schemeof the present disclosure when a terminal moves from a 4G network to a5G network according to an embodiment of the present disclosure;

FIG. 5 is an exemplary flowchart illustrating a method for controlling afirst entity according to an embodiment of the present disclosure; and

FIG. 6 is an exemplary flowchart illustrating a method for controlling afirst network base station according to an embodiment of the presentdisclosure.

DETAILED DESCRIPTION

FIGS. 1 through 6, discussed below, and the various embodiments used todescribe the principles of the present disclosure in this patentdocument are by way of illustration only and should not be construed inany way to limit the scope of the disclosure. Those skilled in the artwill understand that the principles of the present disclosure may beimplemented in any suitably arranged system or device.

Hereinafter, in describing the present disclosure, related well-knownfunctions or configurations incorporated herein are not described indetail in the case where it is determined that they obscure the subjectmatter of the present disclosure in unnecessary detail. Hereinafter,embodiments of the present disclosure will be described in detail withreference to the accompanying drawings.

In describing embodiments in the present description, explanation of thetechnical contents that are well-known in the technical fields to whichthe present disclosure pertains and are not directly related to thepresent disclosure will be omitted in the case where it is determinedthat they obscure the subject matter of the present disclosure inunnecessary detail.

For the same reason, in the accompanying drawings, some constituentelements are exaggerated, omitted, or roughly illustrated. Further,sizes of some constituent elements may not completely reflect the actualsizes thereof. In the drawings, the same drawing reference numerals areused for the same elements across various figures.

The aspects and features of the present disclosure and methods forachieving the aspects and features will be apparent by referring to theembodiments to be described in detail with reference to the accompanyingdrawings. However, the present disclosure is not limited to theembodiments disclosed hereinafter, but can be implemented in diverseforms. The matters defined in the description, such as the detailedconstruction and elements, are nothing but specific details provided toassist those of ordinary skill in the art in a comprehensiveunderstanding of the disclosure, and the present disclosure is onlydefined within the scope of the appended claims. In the entiredescription of the present disclosure, the same drawing referencenumerals are used for the same elements across various figures.

It will be understood that each block of the flowchart illustrations,and combinations of blocks in the flowchart illustrations, can beimplemented by computer program instructions. These computer programinstructions can be provided to a processor of a general purposecomputer, special purpose computer, or other programmable dataprocessing apparatus to produce a machine, such that the instructions,which execute via the processor of the computer or other programmabledata processing apparatus, create means for implementing the functionsspecified in the flowchart block or blocks. These computer programinstructions may also be stored in a computer-usable orcomputer-readable memory that can direct a computer or anotherprogrammable data processing apparatus to function in a particularmanner, such that the instructions stored in the computer-usable orcomputer-readable memory produce an article of manufacture includinginstruction means that implement the function specified in the flowchartblock or blocks. The computer program instructions may also be loadedonto a computer or other programmable data processing apparatus to causea series of operational steps to be performed on the computer or otherprogrammable apparatus to produce a computer implemented process suchthat the instructions that execute on the computer or other programmableapparatus provide steps for implementing the functions specified in theflowchart block or blocks.

Also, each block of the flowchart illustrations may represent a module,segment, or portion of code, which comprises one or more executableinstructions for implementing the specified logical function(s). Itshould also be noted that in some alternative implementations, thefunctions noted in the blocks may occur out of the order. For example,two blocks shown in succession may in fact be executed substantiallyconcurrently or the blocks may sometimes be executed in the reverseorder, depending upon the functionality involved.

The term “˜unit”, as used in an embodiment, means, but is not limitedto, a software or hardware component, such as FPGA or ASIC, whichperforms certain tasks. However, “˜unit” does not mean to be limited tosoftware or hardware. The term “˜unit” may advantageously be configuredto reside on the addressable storage medium and configured to execute onone or more processors. Thus, “˜unit” may include, by way of example,components, such as software components, object-oriented softwarecomponents, class components and task components, processes, functions,attributes, procedures, subroutines, segments of program code, drivers,firmware, microcode, circuitry, data, databases, data structures,tables, arrays, and variables. The functionality provided for in thecomponents and “˜units” may be combined into fewer components and“˜units” or further separated into additional components and “˜units”.Further, the components and “˜units” may be implemented to operate oneor more CPUs in a device or a security multimedia card.

In a wireless communication technology, standardization for 5Gcommunication standards is actively in progress, and it is expected that5G services will start. For some time from an initial introduction, itis expected that a new 5G network for providing 5G services coexistswith the existing established 4G network to provide services to mobilecommunication terminals, and in particular, in order to solve theservice cutoff problem due to the limited service coverage in theinitial stage of 5G introduction, it is essential to consider a functionof providing seamless services in interworking with the 4G network.Further, in case of an ultra-high frequency band (mmW frequency band)being considered as a 5G communication band, it is suitable to broadbandhigh-speed services, but is vulnerable to a path loss with a small cellradius. Accordingly, it is expected that the terminal mobilitymanagement is restricted, and thus there has been a demand for a 4G/5Ginterworking technology to supplement this using the 4G network.

If the terminal intends to change the network to be used throughmovement from a 5G service coverage to a 4G serviceable coverage ormovement from the 4G service coverage to the 5G serviceable coverage,the overall operation and procedure of the terminal and 4G/5G networksto provide seamless services to the terminal may be called the 4G-5Ginterworking, and the 4G-5G interworking may be classified into twotypes: single-registration interworking and dual-registrationinterworking.

The terminal may mean user equipment (UE), mobile station, subscriberstation, remote terminal, wireless terminal, or user device.

Referring to FIG. 1A, according to the single-registration interworkingtype, a terminal 100 may be connected to only one of 4G and 5G networksto perform communication at a certain moment. For example, thesingle-registration interworking type is a type in which, if theterminal moves between the service coverages of the 4G and 5G networks,terminal status information is transferred from the currently connectednetwork to the network to move thereto, and thus the seamless servicesbecome possible. The single-registration interworking type requires anew interface 190 for the interworking operation between the 4G and 5Gnetworks. On the other hand, referring to FIG. 1B, the dual-registrationinterworking is a type in which the terminal maintains a state where theterminal is connected to both the 4G and 5G networks, and if theterminal moves between the service coverages of the 4G and 5G networks,a data forwarding path is reconfigured to enable the terminal to use theseamless communication services. The dual-registration interworking typedoes not require to implement a new interface between the 4G and 5Gnetworks.

The present disclosure relates to a data synchronization scheme between4G and 5G base stations to prevent a packet loss that may occur duringapplication of the dual-registration interworking. Hereinafter,explanation will be made around the dual-registration interworkingrelated to the present disclosure.

According to an embodiment of the present disclosure, in thedual-registration interworking, the terminal may separately performinitial connection processes with the 4G and 5G networks, and theinitial connection processes may be performed in a sequential orsimultaneous manner.

On the other hand, as illustrated in FIGS. 1A and 1B, if the terminal100 accesses the 4G network, it may camp on an LTE base station 110. Amobility management entity (MME) 120 may manage mobile context of theterminal 100, session context, and security information. A servinggateway (SGW) 130 may provide a user plane function. The MME 120 and theSGW 130 may be in the same physical entity.

If the terminal 100 accesses the 5G network, it may camp on an NR basestation 140. In the 5G network, an access & mobility management function(AMF) entity 150 may be included. The AMF entity 150 may have the samefunction as the function of the MME 120 of the 4G network as describedabove, or may perform at least a part of the function. For example, theAMF entity 150 may manage information related to access authorization ofa core network of the terminal 100 and mobility of the terminal 100.

Further, for the 4G-5G interworking, the communication system mayinclude a PGW-U+UPF entity 160 (or UPF+PGW-U entity), PGW-C+SMF entity170 (or SMF+PGW-C entity), and HSS+UDM entity 180 (or UDM+HSS entity).For example, the PGW-U+UPF entity 160 may perform functions of a 4Gnetwork packet data network gateway-user plane (PGW-U) entity and a 5Gnetwork user plane function (UPF) entity. For example, the PGW-U+UPFentity 160 may perform a routing function so that data can betransmitted and received between the terminal 100 and a data network ona user plane, and may perform an anchor function for allocating aninternet protocol (IP) address corresponding to the data network.

The PGW-C+SMF entity 170 may perform functions of a 4G network packetdata network gateway-control plane (PGW-C) entity and a 5G networksession management function (SMF) entity. For example, the PGW-C+SMFentity 170 may generate a session for data transmission between theterminal 100 and the data network through the PGW-U+UPF entity 160, andmay control UPF relocation for changing the PGW-U+UPF entity 160connected to the terminal 100.

The HSS+UDM entity 180 may perform functions of a home subscriber server(HSS) and a 5G network unified data management (UDM) entity. Forexample, the HSS+UDM entity 180 may manage subscriber information.

FIG. 2 is a diagram explaining a dual-registration interworkingoperation in case where a terminal 200 moves from a 5G network servicecoverage to a 4G network coverage. Even in case where a terminal 200moves from a 4G network service coverage to a 5G network servicecoverage, a similar operation is performed, and for convenience inexplanation, detailed explanation thereof will be omitted.

According to an embodiment of the present disclosure, as illustrated inFIG. 2, if a terminal 200, which is initially connected to a 5G network,secedes from the service coverage and moves to a 4G network coverage, itperforms an initial connection with the 4G network (in case where aconnection process was not previously performed), or it performs a PDNconnectivity request procedure (in case where the connection process waspreviously performed). In the terminal connection or PDN connectionconfiguration process, a mobility management entity (MME) of the 4Gnetwork acquires from HSS+UDM an address of PGW-C+SMF used in the 5Gnetwork to configure a data forwarding path to be used by the terminal200, and using this, it proceeds with a process of configuring a defaultbearer to be used by the PGW-C+SMF and the terminal 200. Through such aprocess, it is possible to configure the same PGW-C+SMF and data pathand to maintain the same IP address of the terminal 200 even if theterminal 200 moves between the 4G and 5G networks. If the default bearerof the terminal 200 is configured in the terminal connection process,the PGW-C+SMF switches the data forwarding path from a path in whichdata is transferred to the previous 5G base station to a path in whichthe data is transferred to a new 4G base station.

As described above, the dual-registration interworking is performedthrough an access (or session configuration) procedure to the network towhich the terminal has newly moved (in this case, 4G network), and isfeatured so that an inter-eNB handover signal procedure is notperformed. Accordingly, it is difficult to apply the datasynchronization technology based on the existing inter-eNB handoversignal procedure, and thus a new type of a synchronization method isnecessary.

In general, a handover process between 4G base stations may include thefollowing operations.

1) A source base station accessed by the terminal before the handoverdetermines whether the handover is necessary.2) In case where the handover is necessary, the source base stationtransfers to a target base station a signal message indicating that thehandover of the corresponding terminal is necessary. In this process,the signal message transferred by the source base station includes aseparate forwarding data path setup request information for transmittingdata remaining in the source base station to the target base station. Inthis process, setup of a plurality of forwarding data paths in the unitof an EPS bearer is requested.3) After receiving the handover request message from the source basestation, the target base station determines whether to accept thehandover and whether to accept the forwarding data path setup. In caseof accepting the forwarding data path setup, a tunnel endpoint ID (TEID)of a tunnel for each bearer to which the data is to be transferred isincluded in a response message to be transferred to the source basestation.4) The source base station commands the terminal to start the handover,and transfers the remaining data to the target base station using thetunnels.

The above-described operation describes a general handover processbetween 4G base stations, and includes the contents in which path setupfor data synchronization is performed through handover signaling. If thehandover is performed in the 4G network, the tunnel configuration unitis maintained as the EPS bearer unit, and thus a process for packetreclassification is not required in the source base station. In thiscase, the data can be transferred to the target base station througheach corresponding tunnel for each PDCP buffer previously stored.

In general, information for configuring the data forwarding path for thedata synchronization is transferred through the inter-eNB handoverprocedure, whereas in the dual-registration interworking as describedabove, the terminal mobility is supported by a connection procedurebetween the terminal and the network without transferring the inter-eNBhandover signal, and thus it is not possible to apply the related art.Further, since the 5G network and the 4G network have different units toconfigure the data forwarding paths, it is difficult to apply thetunneling method in the related art as it is. In the 4G network, theforwarding path (tunnel) is configured in the unit of a data radiobearer of a radio section, whereas in the 5G network, the forwardingpath is configured in the unit of QoS flows corresponding to a set of IPflows having the same QoS. Accordingly, it is not possible to apply theexisting method for configuring the forwarding path as it is.

Accordingly, the present disclosure proposes a data synchronizationscheme for supporting the terminal mobility between the 4G and 5Gnetworks without a packet loss through non-use of a handover signalprocedure during application of the dual-registration interworking. Ifthe terminal moves between the 4G and 5G networks through application ofthe scheme proposed in the present disclosure, it becomes possible toprovide seamless services without a data loss.

Specifically, the present disclosure relates to the contents in whichcommunication services are provided to a terminal that can perform dualaccess to the 4G and 5G through the 4G and 5G networks. The terminalseparately accesses the 4G and 5G, and supports a dual-access functionto the 4G and 5G networks. The 4G network is composed of an MME, SGW,and eNB, and PGW-C, PGW-U, and HSS have common functions to the 5Gnetwork. The 5G network is composed of an AMF and an NR base station,and SMF, UPF, and UDM have common functions to the 4G network. The PGW-Cand SMF, the PGW-U and UPF, and the HSS and UDM are implemented to haveone common function, respectively, and are commonly used for the 4G and5G network operations.

As illustrated in FIG. 2, an embodiment of the present disclosureincludes determining, by PGW-C+SMF, QoS flows for data synchronizationin a dual-registration interworking process if a terminal moves between4G and 5G network coverages, configuring a path for transferringremaining data packets between base stations, reclassifying andbuffering, by PGW-U+UPF, the data packets transferred from the basestation, and transferring the buffered packets to a new base station andreleasing the forwarding path.

Further, for operations of new functions proposed by the presentdisclosure, new messages and parameters are defined as follows.

-   -   Forwarding path setup request/response message: This is used to        configure a data forwarding path for data synchronization        between SMF and NR base station or between SMF and 4G base        station (eNB). The SMF transmits the request message. For        example, the SMF may transmit the request message to the UPF.    -   Forwarding path setup request (n-tuples of {QoS flow ID list,        UPF TEID})

(During movement from 5G network to 4G network coverage)

-   -   QoS flow ID list: Information of QoS flows for transferring data        through the same data forwarding path    -   UPF TEID: UPF reception end information (tunnel endpoint ID) for        transferring data from a base station to UPF    -   Forwarding path setup request (n-tuples of {EPS bearer ID, UPF        TEID})

(During movement from 4G network to 5G network coverage)

-   -   EPS bearer ID: Bearer (4G QoS providing unit) information        transferred through a data forwarding path    -   UPF TEID: UPF reception end information (tunnel endpoint ID) for        transferring data from a base station to UPF    -   Forwarding path setup response (list of accepted QoS flow IDs)

(During movement from 5G network to 4G network coverage)

-   -   List of accepted QoS flow IDs: List of QoS flows for which a        data transfer request has been accepted by a 5G base station    -   Forwarding path setup response (list of accepted EPS bearer IDs)

(During a movement from 4G network to 5G network coverage)

-   -   List of accepted EPS bearer IDs: List of EPS bearers for which a        data transfer request has been accepted by a 4G base station

According to an embodiment of the present disclosure, through themovement from the 5G network to the 4G network as shown in FIG. 2, theterminal 200 may transmit an attach request to an LTE base station 210of the 4G network. In this case, the LTE base station 210 may transmitan attach and path establishment request to an IP anchor 220. The IPanchor 220 may include PGW-U+UPF. For example, the LTE base station 210may transmit the attach and path establishment request to the PGW-U+UPFvia the MME and the PGW-C+SMF.

If the IP anchor 220 determines forwarding path establishment, theterminal 200 may transfer a forwarding path setup information list to anNR base station 230 of the 5G network pre-attached by the terminal 200.On the other hand, the NR base station 230 of the 5G network is merelyexemplary, and may also be an enhanced LTE (eLTE).

The NR base station 230 having received the forwarding path setupinformation list may transmit packets, which have been received, buthave not been transmitted to the terminal 200, to the IP anchor 220through a PDU tunnel. The IP anchor 220 may reclassify and buffer thepackets received from the NR base station 230, and then may transmit thepackets to the LTE base station 210 through an EPS bearer.

Further, if the IP anchor 220 receives not only the packets receivedfrom the NR base station 230 but also new packets to be transmitted tothe terminal 200, it may transmit the new packets after transmitting allthe packets received from the NR base station 230 to the LTE basestation 210. However, this is merely exemplary, and the IP anchor 220may transmit the packets received from the NR base station 230 and thenew packets to the LTE base station 210 based on a separately configuredpriority.

According to an embodiment, the IP anchor 220 may separately manage abuffer for the packets received and forwarded from the NR base station230 and a buffer for the new packets. Further, the respective buffers ofthe IP anchor 220 may transmit the packets to a buffer for the forwardedpackets of the LTE base station 210 and a buffer for the new packet,respectively. Further, if the LTE base station 210 receiving the packetsincludes a single buffer although the IP anchor 220 separately managesthe respective buffers, the respective buffers of the IP anchor 220 maytransmit the packets to the buffer of the LTE base station 210sequentially or based on the priority.

Based on the above-described contents, the detailed operation ofconstituent elements according to the present disclosure is asillustrated in FIG. 3. FIG. 3 is a diagram illustrating a dataforwarding path setup operation procedure that is a process in which aterminal moves from a 5G network to a 4G network.

Based on FIG. 3, the detailed operations for data forwarding in casewhere a terminal moves from a 5G network to a 4G network will bedescribed as follows.

(1) After an MME 330 receives an attach request of a terminal 300, itmay transfer a session creation request for data transmission toSMF+PGW-C 360. The SMF+PGW-C 360 may select QoS flows to which datasynchronization is to be applied based on 5G session information storedtherein, and include an indicator for requesting forwarding path setupin the unit of a PDU session, for data synchronization with respect tothe corresponding QoS flow, in an Sx session modification message to betransferred to UPF+PGW-U 370.

According to an embodiment, the terminal 300 may perform wirelesscommunication in the 5G network. For example, at operation S300, theterminal 300 may transmit and receive data through UPF+PGW-U 370 and PDUsessions.

At operation S301, the terminal 300 may discover an evolved universalterrestrial radio access network (E-UTRAN) 310 that is a 4G basestation, and may determine a handover procedure. For example, through amovement of the terminal 300, the terminal 300 may release an attach tothe 5G network, and may determine a handover to the E-UTRAN 310. Atoperation S302, the terminal 300 may transmit an attach request to theE-UTRAN 310. At operation S303, the E-UTRAN 310 may transmit the attachrequest to the MME 330.

At operation S304, an authentication/security procedure between theterminal 300 and the MME 330 and an authentication/security procedurebetween the MME 330 and UDM+HSS 390 may be performed. Further, atoperation S305, location update between the MME 330 and the UDM+HSS 390may be performed.

At operation S306, the MME 330 having received the attach request maytransmit a session creation request to an SGW 350. Further, at operationS307, the SGW 350 may transmit the session creation request to SMF+PGW-C360. At operation S308, the SMF+PGW-C 360 may determine data forwardingbased on 5G session information.

(2) UPF+PGW-C 370 allocates forwarding path resources (forwarding pathTEIDs) for data synchronization with respect to the QoS flows requestedfrom the SNF+PGW-C 360 in the unit of a PDU session, and then includescorresponding information in a response message to be transmitted to theSMF+PGW-C 360.

For example, at operation S309, the SMF+PGW-C 360 may transfer a messageincluding an indicator for requesting forwarding path setup in the unitof a PDU session to UPF+PGW-U 370. For example, the SMF+PGW-C 360 mayselect QoS flows to which data synchronization is to be applied based onthe pre-stored 5G session information, and include an indicator forrequesting forwarding path setup in the unit of a PDU session, for datasynchronization with respect to the corresponding QoS flow, in an Sxsession modification message to be transmitted to the UPF+PGW-U 370.Further, the UPF+PGW-U 370 may transmit a response message to theSMF+PGW-C 360.

(3) After performing the Sx session modification procedure, theUPF+PGW-C 360 interrupts packet transfer to the 5G base station, andstores packets newly received from an external network in buffers forQoS flows (or stores packets in buffers for 5G QoS flows depending onimplementations). For example, at operation S310, the UPF+PGW-U 370 maystart buffering.

According to another embodiment of the present disclosure, it is alsopossible for the UPF+PGW-U 370 to continuously transfer the receivedpackets to the NG-RAN 320 that is a 5G base station, instead ofperforming the buffering, until the setup of the data forwarding pathwith the E-UTRAN 310 that is a 4G base station is completed (in thiscase, the amount of data packets to be transferred from the NG-RAN 320to the E-UTRAN 310 through the forwarding path is increased).

(4) The SMF+PGW-C 360 transfers the forwarding path setup requestmessage including the forward path TEID information transferred from theUPF_PGW-U 370 to an NG-RAN 320 that is the 5G base station, and theNR-RAN 320 determines whether to accept the data synchronization requestwith respect to the requested QoS flow list, and transfers the result ofthe determination to the SMF+PGW-C 360. The SMF+PGW-C 360 reports thecorresponding information to the UPF+PGW-U 370. For example, atoperation S311, the SMF+PGW-C 360 may transmit a session creationresponse to the SGW 350. Further, at operation S312, the SMF+PGW-C 360may transfer the forwarding path setup request message to the NG-RAN320. The 5G base station may transfer a response message to theforwarding path setup request message to the SMF+PGW-C 360.

(5) The NG-RAN 320 transmits the packets of the corresponding terminal300, which remain without being transmitted, to the correspondingaddress of the UPF+PGW-U 370 through forwarding paths for PDU sessionsmapped to the QoS flows using the forwarding path TEID informationtransferred from the SMF+PGW-U 370. The NG-RAN 320 transfers to theUPF+PGW-U 370 a separate packet for notifying that the final packet hasbeen transferred in the process of transferring the last remainingpacket.

For example, at operation S313, the SGW 350 having received the sessioncreation response may transfer the session creation response to the MME330. Further, at operation S314, the NG-RAN 320 may determine whether toforward the remaining packets that have not been transmitted to theterminal 300. If the data forwarding is determined, the NG-RAN 320 mayforward the remaining non-transmitted packets to the UPF+PGW-U 370. Inthis case, if the remaining non-transmitted packets are transmitted inall, the NG-RAN 320 may transfer even the final packet for notifyingthat all the remaining packets have been forwarded to the UPF+PGW-U 370.

(6) The UPF+PGW-U 370 reclassifies the packets received from the NG-RAN320 through the forwarding paths for the data synchronization forbearers of the 4G network, and stores the reclassified packets inbuffers for bearers. If a separate packet notifying that the finalpacket has been transferred is transferred from the NG-RAN 320, theUPF+PGW-U 370 may release the forwarding paths set for the datasynchronization, and may selectively release the forwarding paths aftera predetermined time depending on implementations.

Depending on the implementations, the separate packet may be stored in aseparate buffer together with newly received packets, or may be storedusing the same buffer as that newly received. This is unrelated to thebasic principle of the present disclosure.

For example, at operation S315, the UPF+PGW-U 370 may performreclassification and buffering. The UPF+PGW-U 370 may receive thepackets from the NG-RAN 320 through forwarding paths for the QoS flows.The UPF+PGW-U 370 may reclassify the received packets for bearers of the4G network. Further, the UPF+PGW-U 370 may map the reclassified packetsfor bearers to transmit the packets in the unit of a bearer with respectto the e-UTRAN 310.

(7) If the terminal 300 completes the path setup with the E-UTRAN 310and the setup of the data forwarding paths of the 4G network iscompleted, the UPF+PGW-U 370 transfers the packets transferred from theNG-RAN 320 and stored in the buffers for the data synchronization to theterminal 300 through the E-UTRAN 310. If forwarding of the packetsstored in the synchronization buffers is completed, forwarding of thepackets stored in the buffers in which the newly transferred packets arestored starts.

For example, in order for the terminal 300 to complete the path setupwith the E-UTRAN 310, at operation S316, the MME 330 may transmit aninitial context configuration request to the E-UTRAN 310. Further, atoperation S317, the terminal 300 and the E-UTRAN 310 may perform RRCconnection reconfiguration. Further, at operation S319, the terminal 300may transmit a direct transfer to the E-UTRAN 310. At operation S321,the terminal 300 may transmit initial uplink data to the UPF+PGW-U 370through the SGW 350. Further, at operation S322, the MME 330 and theUPF+PGW-U 370 may correct the bearer. At operation S323, the UPF+PGW-U370 may forward the packets transferred from the NG-RAN 320 and bufferedto the terminal 300.

According to another embodiment of the present disclosure, FIG. 4 is adiagram illustrating a data forwarding path setup operation procedure.For example, FIG. 4 is a diagram illustrating a process during amovement from a 4G network to a 5G network.

Based on FIG. 4, the detailed operation for data forwarding in casewhere a terminal moves from a 4G network to a 5G network will bedescribed as follows.

(1) If a session creation request for data transmission is transferredto SMF+PGW-C 450 after an AMF 430 receives an attach request of aterminal 400, the SMF+PGW-C 450 selects 4G EPS bearers to which datasynchronization is to be applied based on 4G session information storedtherein, includes an indicator for requesting forwarding path setup inthe unit of a 4G EPS bearer, for data synchronization with respect tothe corresponding EPS bearer, in an N4 sessionestablishment/modification request message, and transfers the message toUPF+PGW-U 440.

According to an embodiment, the terminal 400, which accesses an evolveduniversal terrestrial radio access network (E-UTRAN) 420 and performswireless communication in the 4G network, may discover an NR-RAN 410,and may perform a handover. For example, through movement of theterminal 400, the terminal 400 may release an attach to the 4G network,and may determine a handover to the NR-RAN 410. For the handover to the5G network, the terminal 400, at operation S400, may transmit a PDUsession establishment request to the AMF 430.

At operation S401, the AMF 430 may transfer the received PDU sessionestablishment request to the SMF+PGW-C 450. Further, at operation S402,the SMF+PGW-C 450 may determine whether to perform data forwarding basedon stored 4G session information. Further, at operation S403, theSMF+PGW-C 450 may transmit to UPF+PGW-U 440 a message including anindicator for requesting setup of a forwarding path in the unit of a 4GEPS bearer.

(2) The UPF+PGW-U 440 allocates forwarding path resources (forwardingpath TEIDs) for data synchronization with respect to the 4G EPS bearersrequested from the SMF+PGW-C 450 in the unit of a 4G EPS bearer,includes corresponding allocation information in a response message, andtransfers the response message to the SMF_PGW-C 450. For example, atoperation S404, the UPF+PGW-U 440 may transmit the response message tothe SMF+PGW-C 450.

(3) After performing the N4 session establishment/modificationprocedure, the UPF+PGW-U 440 interrupts packet transfer to the E-UTRAN420, and stores packets newly received from an external network inbuffers for 4G EPS bearers (or in buffers for 5G QoS flows depending onimplementations). For example, at operation S405, the UPF+PGW-U 440 maystart buffering.

According to another embodiment of the present disclosure, it is alsopossible for the UPF+PGW-U 440 to continuously transfer the receivedpackets to the E-UTRAN 420 that is a 4G base station, instead ofperforming the buffering, until the setup of the data forwarding pathwith the NR-RAN 410 that is a 5G base station is completed (in thiscase, the amount of data packets to be transferred from the 4G basestation to the 5G base station through the forwarding path isincreased).

(4) The SMF+PGW-C 450 transfers the forwarding path setup requestmessage including the forward path TEID information transferred from theUPF+PGW-U 440 to the E-UTRAN 420, and the E-UTRAN 420 determines whetherto accept the data synchronization request with respect to the requestedEPS bearer, and transfers the result of the determination to theSMF+PGW-C 450. The SMF+PGW-C 450 reports the corresponding informationto the UPF+PGW-C 440. For example, at operation S406, the SMF+PGW-C 450may transmit a PDU session establishment accept response to the AMF 430.Further, at operation S407, the SMF+PGW-C 450 may transfer theforwarding path setup request message to the E-UTRAN 420. The E-UTRAN420 may transfer a response message to the forward path setup requestmessage to the SMF+PGW-C 450.

(5) The E-UTRAN 420 transmits the remaining non-transmitted packets ofthe corresponding terminal to the corresponding address of the UPF+PGW-U440 using the forwarding path TEID information configured in the unit ofa 4G EPS bearer and transferred from the SMF+PGW-C 450. The E-UTRAN 420transfers to the UPF+PGW-U 440 a separate packet for notifying that thefinal packet has been transferred in the process of transferring thelast remaining packet.

For example, at operation S408, the E-UTRAN 420 may determine whether toforward the remaining non-transmitted packets to the terminal 400. Ifthe data forwarding is determined, the E-UTRAN 420 may forward theremaining non-transmitted packets to the UPF+PGW-U 440. In this case, ifthe remaining non-transmitted packets are transmitted in all, theE-UTRAN 420 may transfer even the final packet for notifying that allthe remaining packets have been forwarded to the UPF+PGW-U 440.

(6) The UPF+PGW-U 440 reclassifies the packets received from the E-UTRAN420 through the forwarding paths for the data synchronization for QoSflows of the 5G network, and stores the reclassified packets in buffersfor QoS flows (or depending on implementations, buffers for PDU sessionscan be used). If a separate packet notifying that the final packet hasbeen transferred is transferred from the E-UTRAN 420, the UPF+PGW-U 440may release the forwarding paths set for the data synchronization, andmay selectively release the forwarding paths after a predetermined timedepending on implementations.

Depending on the implementations, the separate packet may be stored in aseparate buffer together with newly received packets, or may be storedusing the same buffer as that newly received. This is unrelated to thebasic principle of the present disclosure.

For example, at operation S409, the UPF+PGW-U 440 may performreclassification and buffering. The UPF+PGW-U 440 may receive thepackets from the E-UTRAN 420 through forwarding paths for the 4G EPSbearers. The UPF+PGW-U 440 may reclassify the received packets for QoSflows of the 5G network. Further, the UPF+PGW-U 440 may map thereclassified packets for QoS flows to transmit the packets in the unitof a QoS flow with respect to the NG-RAN 410.

(7) If the terminal 400 completes the path setup with the NG-RAN 410 andthe setup of the data forwarding paths of the 5G network is completed,the UPF+PGW-U 440 transfers the packets transferred from the E-UTRAN 420and stored in the buffers for the data synchronization to the terminalthrough the NG-RAN 410. If forwarding of the packets stored in thesynchronization buffers is completed, forwarding of the packets storedin the buffers in which the newly transferred packets are stored starts.

For example, at operation S410, the AMF 430 may transmit an N2 PDUsession request to the NG-RAN 410. At operation S411, the terminal 400and the NG-RAN 410 may configure RAN-specific resources. At operationS412, the NG-RAN 410 may transmit an ack message for the N2 PDU sessionrequest to the AMF 430. At operation S413, the terminal 400 havingaccessed the 5G network may transmit initial uplink data to theUPF+PGW-U 440. If the bearer between the AMF 430 and the SMF+PGW-C 450is corrected at operation S 414, the SMF+PGW-C 450, at operation S415,may transmit an IP v6 address configuration to the terminal 400 throughthe UPF+PGW-U 440. Further, at operation S416, the UPF+PGW-U 440 mayforward the packets transferred from the E-UTRAN 420 and buffered to theterminal 400.

According to embodiments of the present disclosure, in relation to anapparatus and an operation for providing data synchronization duringmovement between a 4G network and a 5G network for a 4G/5Gdual-registered mobile communication terminal, the present disclosurediscloses determining, by a node taking charge of an anchor (PGW-C+SMF),QoS flows for data synchronization in a data signaling forwarding path,configuring a path for transferring remaining data packets between basestations, reclassifying and buffering, by a node taking charge of ananchor (PGW-U+UPF), the data packets transferred from a source basestation in the IP packet forwarding path before transferring the datapackets to a target base station, transferring, by the node takingcharge of the anchor (PGW-U+UPF), the buffered packets to a new basestation in the IP packet forwarding path, and determining a time torelease the forwarding path for data transfer and releasing theforwarding path.

According to the present disclosure as described above, it is possibleto transfer the remaining data between different base stations in thedual-registration interworking process, and thus it becomes possible toprovide the terminal mobility between the 4G and 5G networks without thedata loss.

Further, it becomes possible to provide the terminal mobility with nodata loss without changing the 5G and 4G base station implementationthrough addition of a simple function of new equipment, such as SMF andUPF.

Further, it becomes possible to support different QoS and forwardingpath units in the 5G and 4G networks without changing the 5G and 4G basestation functions.

Further, it becomes possible to exempt additional functionimplementation costs for re-ordering in the terminal and the networkthrough in-order delivery of the packets to the terminal withoutchanging the packet order during the 4G-5G network movement.

FIG. 5 is a flowchart illustrating a method for controlling a firstentity according to an embodiment of the present disclosure.

First, at operation S500, in case of a handover from a first network toa second network, a first entity may receive a data forwarding requestfrom a second entity. The first entity may be an entity that processesuser data packets, and the second entity may be an entity that processescontrol signals. For example, the first entity may be UPF+PGW-U entity,and the second entity may be SMF+PGW-C entity.

At operation S510, based on the received data forwarding request, thefirst entity may configure a data forwarding path between the firstentity and a first network base station.

At operation S520, the first entity may transmit information on theconfigured data forwarding path to the first network base station. Incase where the terminal performs a handover from the 5G network to the4G network, the first network base station may be a 5G base station. Incontrast, in case where the terminal performs a handover from the 4Gnetwork to the 5G network, the first network base station may be a 4Gbase station.

At operation S530, based on the configured data forwarding path, thefirst entity may receive data packets from the first network basestation. For example, if the first network base station is the 5G basestation, through the handover of the terminal, the 5G base station maytransmit the remaining packets that have not been transmitted to theterminal to forwarding paths for PDU sessions mapped to QoS flows.Further, if the remaining non-transmitted packets are transmitted inall, the 5G base station may transmit the final packet indicating thatall the data packets have been transmitted to the first entity. On theother hand, if the first network base station is the 4G base station,through the handover of the terminal, the 4G base station may transmitthe remaining packets that have not been transmitted to the terminal toforwarding paths established in the unit of a 4G EPS bearer. Further, ifthe remaining non-transmitted packets are transmitted in all, the 4Gbase station may transmit the final packet indicating that all the datapackets have been transmitted to the first entity.

If the final packet is received, the first entity may release the dataforwarding path configured between the first entity and the firstnetwork base station.

At operation S540, the first entity may forward the received datapackets through a path established with respect to a second network basestation.

The first entity may perform buffering of the data packets received fromthe first network base station. For example, the first entity may storethe data packets received from the first network base station in a firstbuffer, and may store new data packets in a second buffer. Further, thefirst entity may transmit the data packets stored in the first buffer tothe second network base station, and if transmission of the data packetsstored in the first buffer is completed, the first entity may transmitthe data packets stored in the second buffer to the second network basestation. However, this is merely exemplary, and the first entity maytransmit the data packets stored in the first buffer and the secondbuffer to the second network base station based on a predeterminedpriority.

Further, the first entity may reclassify the received data packets, andmay map the reclassified data packets based on the path established withrespect to the second network base station. The reclassification mayreclassify the received data packets for bearers if the second networkbase station is the 4G base station, and may reclassify the receiveddata packets for QoS flows if the second network base station is the 5Gbase station.

On the other hand, FIG. 6 is a flowchart illustrating a method forcontrolling a first network base station according to an embodiment ofthe present disclosure.

At operation S600, if a first entity receives a data forwarding requestfrom a second entity in case where a terminal performs a handover from afirst network to a second network, a first network base station mayreceive configuration information on a data forwarding path between thefirst entity and the first network base station from the first entitybased on the received data forwarding request. The first entity may bean entity that processes user data packets, and the second entity may bean entity that processes control signals. For example, the first entitymay be UPF+PGW-U entity, and the second entity may be SMF+PGW-C entity.

At operation S610, based on the configuration information, the firstnetwork base station may establish the data forwarding path. Forexample, the first network base station may establish the dataforwarding path between the first entity and a first network basestation.

At operation S620, the first network base station may transmit the datapackets that are not transmitted to the terminal to the first entitythrough the established data forwarding path. As the terminal performs ahandover from the first network to the second network, the first networkbase station may transmit the data packets that are not transmitted tothe terminal to the first entity through the established data forwardingpath.

The data packets may be forwarded through the path established withrespect to a second network base station by the first entity.

If the data packets stored in the first network base station aretransmitted in all, the first network base station may transmit thefinal packet indicating that all the stored data packets have beentransmitted to the first entity. Further, if the final packet istransmitted to the first entity, the data forwarding path configuredbetween the first entity and the first network base station may bereleased by the first entity.

According to an embodiment of the present disclosure, a first entity mayreceive a data forwarding request from a second entity through amovement of a terminal from a first network to a second network,configure a data forwarding path between the first entity and a firstnetwork base station based on the received data forwarding request andtransmit information on the configured data forwarding path to the firstnetwork base station, receive data packets from the first network basestation based on the configured data forwarding path, and forward thereceived data packets through a path established with respect to asecond network base station.

The first entity may be configured to buffer the data packets receivedfrom the first network base station.

The first entity may be configured to reclassify the received datapackets for bearers if the second network base station is a 4G basestation, reclassify the received data packets for QoS flows if thesecond network base station is a 5G base station, and map thereclassified data packets based on a path established with respect tothe second network base station.

The first entity may be configured to store the data packets receivedfrom the first network base station and new data packets in differentbuffers.

The first entity may be configured to transmit the data packets receivedfrom the first network base station and stored to the second networkbase station, and transmit the new stored data packets to the secondnetwork base station if the forwarding is completed.

The first entity may be configured to receive a final packet indicatingthat all the stored data packets have been transmitted from the firstnetwork base station.

The first entity may be configured to release the data forwarding pathconfigured between the first entity and the first network base stationif the final packet is received.

The first entity may be an entity processing user data packets, and thesecond entity may be an entity processing control signals.

According to another embodiment of the present disclosure, a firstnetwork base station may be configured to receive, if a first entityreceives a data forwarding request from a second entity through movementof a terminal from a first network to a second network, configurationinformation on a data forwarding path between the first entity and thefirst network base station from the first entity based on the receiveddata forwarding request, establish the data forwarding path based on theconfiguration information, and transmit data packets that have not beentransmitted to the terminal to the first entity through the establisheddata forwarding path, wherein the data packets are forwarded by thefirst entity through a path established with respect to a second networkbase station.

The first network base station may be configured to transmit a finalpacket indicating that all the stored data packets have been transmittedto the first entity and release the data forwarding path configuredbetween the first entity and the first network base station if all thedata packets stored in the first network base station have beentransmitted.

The first entity may be an entity processing user data packets, and thesecond entity may be an entity processing control signals.

In the embodiments of the present disclosure as described above,constituent elements included in the present disclosure are expressed ina singular form or in a plural form. However, such a singular or pluralexpression is selected to suit a situation presented for convenience inexplanation, and thus the present disclosure is not limited to suchsingular or plural constituent elements. Even plural constituentelements may be expressed in a singular form, and even a singleconstituent element may be expressed in a plural form.

Although detailed embodiments of the present disclosure have beendescribed in the specification and drawings, it will be apparent thatvarious modifications are possible within the scope of the presentdisclosure. Accordingly, the scope of the present disclosure should notbe limited to the embodiments as described above, but should be definedby the appended claims below and those equivalent to the scope of theclaims.

Although the present disclosure has been described with variousembodiments, various changes and modifications may be suggested to oneskilled in the art. It is intended that the present disclosure encompasssuch changes and modifications as fall within the scope of the appendedclaims.

What is claimed is:
 1. A method for controlling a first entity in awireless communication system, comprising: receiving a data forwardingrequest from a second entity through a movement of a terminal from afirst network to a second network; configuring a data forwarding pathbetween the first entity and a first network base station based on thereceived data forwarding request, and transmitting information on theconfigured data forwarding path to the first network base station;receiving data packets from the first network base station based on theconfigured data forwarding path; and forwarding the received datapackets through a path established with respect to a second network basestation.
 2. The method of claim 1, further comprising buffering the datapackets received from the first network base station.
 3. The method ofclaim 1, further comprising: reclassifying the received data packets;and mapping the reclassified data packets based on a path establishedwith respect to the second network base station, wherein thereclassifying the received data packets reclassifies the received datapackets for bearers if the second network base station is a 4G basestation, and reclassifies the received data packets for QoS flows if thesecond network base station is a 5G base station.
 4. The method of claim1, further comprising storing the data packets received from the firstnetwork base station and new data packets in different buffers.
 5. Themethod of claim 4, wherein the forwarding the received data packetstransmits the data packets received from the first network base stationand stored to the second network base station, and transmits the newstored data packets to the second network base station if the forwardingis completed.
 6. The method of claim 1, wherein the receiving the datapacket further comprises receiving a final packet indicating that allthe stored data packets have been transmitted from the first networkbase station if the data packets stored in the first network basestation have been received in all.
 7. The method of claim 6, furthercomprising releasing the data forwarding path configured between thefirst entity and the first network base station if the final packet isreceived.
 8. The method of claim 1, wherein the first entity is anentity that is processing user data packets, and the second entity is anentity that is processing control signals.
 9. A method for controlling afirst network base station in a wireless communication system,comprising: receiving, if a first entity receives a data forwardingrequest from a second entity through a movement of a terminal from afirst network to a second network, configuration information on a dataforwarding path between the first entity and the first network basestation from the first entity based on the received data forwardingrequest; establishing the data forwarding path based on theconfiguration information; and transmitting data packets that have notbeen transmitted to the terminal to the first entity through theestablished data forwarding path, wherein the data packets are forwardedby the first entity through a path established with respect to a secondnetwork base station.
 10. The method of claim 9, further comprising:transmitting a final packet indicating that all the stored data packetshave been transmitted to the first entity if the data packets stored inthe first network base station have been transmitted in all; andreleasing the data forwarding path configured between the first entityand the first network base station, wherein the first entity is anentity processing user data packets, and the second entity is an entityprocessing control signals.
 11. A first entity in a wirelesscommunication system is configured to: receive a data forwarding requestfrom a second entity through a movement of a terminal from a firstnetwork to a second network, configure a data forwarding path betweenthe first entity and a first network base station based on the receiveddata forwarding request and transmit information on the configured dataforwarding path to the first network base station, receive data packetsfrom the first network base station based on the configured dataforwarding path, and forward the received data packets through a pathestablished with respect to a second network base station.
 12. The firstentity of claim 11, wherein the first entity is configured to buffer thedata packets received from the first network base station.
 13. The firstentity of claim 11, wherein the first entity is configured to reclassifythe received data packets for bearers if the second network base stationis a 4G base station, reclassify the received data packets for QoS flowsif the second network base station is a 5G base station, and map thereclassified data packets based on a path established with respect tothe second network base station.
 14. The first entity of claim 11,wherein the first entity is configured to store the data packetsreceived from the first network base station and new data packets indifferent buffers.
 15. The first entity of claim 14, wherein the firstentity is configured to: transmit the data packets received from thefirst network base station and stored to the second network basestation; and transmit the new stored data packets to the second networkbase station if the forwarding is completed.
 16. The first entity ofclaim 11, wherein the first entity is configured to receive a finalpacket indicating that all the stored data packets have been transmittedfrom the first network base station if the data packets stored in thefirst network base station have been received in all.
 17. The firstentity of claim 16, wherein the first entity is configured to releasethe data forwarding path configured between the first entity and thefirst network base station if the final packet is received.
 18. Thefirst entity of claim 11, wherein the first entity is an entity that isprocessing user data packets, and the second entity is an entity that isprocessing control signals.
 19. A first network base station in awireless communication system is configured to: receive, if a firstentity receives a data forwarding request from a second entity through amovement of a terminal from a first network to a second network,configuration information on a data forwarding path between the firstentity and the first network base station from the first entity based onthe received data forwarding request; establish the data forwarding pathbased on the configuration information; and transmit data packets thathave not been transmitted to the terminal to the first entity throughthe established data forwarding path, wherein the data packets areforwarded by the first entity through a path established with respect toa second network base station.
 20. The first network base station ofclaim 19, wherein the first network base station is configured to:transmit a final packet indicating that all the stored data packets havebeen transmitted to the first entity if the data packets stored in thefirst network base station have been transmitted in all; and release thedata forwarding path configured between the first entity and the firstnetwork base station; wherein the first entity is an entity processinguser data packets, and the second entity is an entity processing controlsignals.